The Experts below are selected from a list of 108 Experts worldwide ranked by ideXlab platform

Kessissoglou N - One of the best experts on this subject based on the ideXlab platform.

  • Active acoustic cloaking of cylindrical shells in low Mach number flow
    'Elsevier BV', 2020
    Co-Authors: Kerferd B, Karimi M, Eggler D, Kessissoglou N
    Abstract:

    The vibro-acoustic responses of a two-dimensional cylindrical shell in low Mach number flow are herein derived. The analytical model takes into account the structural elasticity and coupling of the shell vibration with its interior and exterior acoustic fields in the presence of a moving fluid. The cylindrical shell is modelled using Donnell-Mushtari theory. Taylor transformations are employed to transfer the Convected Wave Equation into the ordinary Wave Equation which was then solved using scattering theory. Three excitation cases corresponding to a plane Wave, an external monopole source and a radial point force applied directly to the shell are considered. Shell circumferential resonances and interior acoustic resonances are identified. Two active control strategies are then applied to acoustically cloak the cylindrical shell at its acoustic and structural resonances. The first control approach employs acoustic control sources in the exterior fluid domain. In the second approach, control forces are applied to directly excite the elastic shell, whereby the structural response is actively modified to manipulate the scattered and radiated acoustic fields arising from plane Wave excitation of the shell. Results show that the second approach is superior in terms of both reduced control effort and cloaking of the global exterior domain. For both control approaches, the performance of the active cloak is shown to deteriorate if the Convected flow field is not accounted for in the control process

  • Acoustic scattering for rotational and translational symmetric structures in nonuniform potential flow
    2017
    Co-Authors: Karimi M, Croaker P, Peake N, Kessissoglou N
    Abstract:

    © Copyright 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. An efficient approach is proposed to predict acoustic scattering with nonuniform potential flow effects for structures with rotational and translational symmetries. The Convected Wave Equation is transformed to Helmholtz and Laplace Equations using a time transformation. The boundary-element method is used to formulate scattering by rotationally symmetric structures as two separate block circulant matrix Equations and, similarly, as two separate block Toeplitz matrix Equations for structures with translational symmetry. Discrete Fourier transform is employed to solve the block circulant systems. The block Toeplitz systems are solved using the generalized minimal residual method along with the discrete Fourier transform. Solving the Convected Wave Equation using structured matrices significantly reduces computational time and storage requirements. To demonstrate the application of the formulation, two exterior acoustic case studies are considered. The first case study examines acoustic scattering from a sphere submerged in potential flow under monopole source excitation. Directivity plots obtained using the proposed technique are compared with analytical results. The second case study examines flow-induced noise generated by a rigid cylinder immersed in low-Mach-number flow, with the effect of mean flow on the scattered acoustic field taken into account using nonuniform potential flow. The fluctuating flowfield is obtained using an incompressible computational fluid dynamics solver. Acoustic sources based on Lighthill's analogy are extracted from the flowfield data using a high-order reconstruction scheme. Results from the hybrid computational fluid dynamics-boundaryelement method technique are presented for turbulent flow past the cylinder, with Reynolds number based on cylinder diameter of ReD = 46;000 and Mach numberM = 0.21. The aeroacoustic results are compared with data from literature

  • Aeroacoustic analysis of a cylinder in low mach number flow using a periodic CFD-BEM technique
    2016
    Co-Authors: Karimi M, Croaker P, Kessissoglou N, Peake N
    Abstract:

    © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The flow-induced noise generated by a rigid cylinder immersed in low Mach number flow is predicted using a hybrid computational fluid dynamics (CFD)-boundary element method (BEM) technique. The fluctuating flow field is obtained using an incompressible CFD solver. A high-order reconstruction scheme is used to extract acoustic sources based on Lighthill's acoustic analogy from the flow field data. The Convected Wave Equation is transformed to Helmholtz and Laplace Equations, with the effect of the mean flow on the scattered acoustic field taken into account using non-uniform potential flow. A periodic BEM technique is used to formulate the acoustic problem as two separate block Toeplitz systems. Solving the aeroacoustic problem using block Toeplitz systems significantly reduces computational time and storage requirements. The generalized minimal residual method is then employed along with the discrete Fourier transform to solve the block Toeplitz systems. The results from the hybrid CFD-BEM technique are presented for turbulent flow past a circular cylinder, with Reynolds number based on the cylinder diameter of ReD= 46000 and Mach number M=0.21. The aeroacoustic results are compared with experimental data from literature

  • Aeroacoustic analysis of a cylinder in low mach number flow using a periodic CFD-BEM technique
    2016
    Co-Authors: Karimi M, Croaker P, Kessissoglou N, Peake N
    Abstract:

    The flow-induced noise generated by a rigid cylinder immersed in low Mach number flow is predicted using a hybrid computational fluid dynamics (CFD)-boundary element method (BEM) technique. The fluctuating flow field is obtained using an incompressible CFD solver. A high-order reconstruction scheme is used to extract acoustic sources based on Lighthill's acoustic analogy from the flow field data. The Convected Wave Equation is transformed to Helmholtz and Laplace Equations, with the effect of the mean flow on the scattered acoustic field taken into account using non-uniform potential flow. A periodic BEM technique is used to formulate the acoustic problem as two separate block Toeplitz systems. Solving the aeroacoustic problem using block Toeplitz systems significantly reduces computational time and storage requirements. The generalized minimal residual method is then employed along with the discrete Fourier transform to solve the block Toeplitz systems. The results from the hybrid CFD-BEM technique are presented for turbulent flow past a circular cylinder, with Reynolds number based on the cylinder diameter of ReD= 46000 and Mach number M=0.21. The aeroacoustic results are compared with experimental data from literature

Karimi M - One of the best experts on this subject based on the ideXlab platform.

  • Active acoustic cloaking of cylindrical shells in low Mach number flow
    'Elsevier BV', 2020
    Co-Authors: Kerferd B, Karimi M, Eggler D, Kessissoglou N
    Abstract:

    The vibro-acoustic responses of a two-dimensional cylindrical shell in low Mach number flow are herein derived. The analytical model takes into account the structural elasticity and coupling of the shell vibration with its interior and exterior acoustic fields in the presence of a moving fluid. The cylindrical shell is modelled using Donnell-Mushtari theory. Taylor transformations are employed to transfer the Convected Wave Equation into the ordinary Wave Equation which was then solved using scattering theory. Three excitation cases corresponding to a plane Wave, an external monopole source and a radial point force applied directly to the shell are considered. Shell circumferential resonances and interior acoustic resonances are identified. Two active control strategies are then applied to acoustically cloak the cylindrical shell at its acoustic and structural resonances. The first control approach employs acoustic control sources in the exterior fluid domain. In the second approach, control forces are applied to directly excite the elastic shell, whereby the structural response is actively modified to manipulate the scattered and radiated acoustic fields arising from plane Wave excitation of the shell. Results show that the second approach is superior in terms of both reduced control effort and cloaking of the global exterior domain. For both control approaches, the performance of the active cloak is shown to deteriorate if the Convected flow field is not accounted for in the control process

  • Acoustic scattering for rotational and translational symmetric structures in nonuniform potential flow
    2017
    Co-Authors: Karimi M, Croaker P, Peake N, Kessissoglou N
    Abstract:

    © Copyright 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. An efficient approach is proposed to predict acoustic scattering with nonuniform potential flow effects for structures with rotational and translational symmetries. The Convected Wave Equation is transformed to Helmholtz and Laplace Equations using a time transformation. The boundary-element method is used to formulate scattering by rotationally symmetric structures as two separate block circulant matrix Equations and, similarly, as two separate block Toeplitz matrix Equations for structures with translational symmetry. Discrete Fourier transform is employed to solve the block circulant systems. The block Toeplitz systems are solved using the generalized minimal residual method along with the discrete Fourier transform. Solving the Convected Wave Equation using structured matrices significantly reduces computational time and storage requirements. To demonstrate the application of the formulation, two exterior acoustic case studies are considered. The first case study examines acoustic scattering from a sphere submerged in potential flow under monopole source excitation. Directivity plots obtained using the proposed technique are compared with analytical results. The second case study examines flow-induced noise generated by a rigid cylinder immersed in low-Mach-number flow, with the effect of mean flow on the scattered acoustic field taken into account using nonuniform potential flow. The fluctuating flowfield is obtained using an incompressible computational fluid dynamics solver. Acoustic sources based on Lighthill's analogy are extracted from the flowfield data using a high-order reconstruction scheme. Results from the hybrid computational fluid dynamics-boundaryelement method technique are presented for turbulent flow past the cylinder, with Reynolds number based on cylinder diameter of ReD = 46;000 and Mach numberM = 0.21. The aeroacoustic results are compared with data from literature

  • Aeroacoustic analysis of a cylinder in low mach number flow using a periodic CFD-BEM technique
    2016
    Co-Authors: Karimi M, Croaker P, Kessissoglou N, Peake N
    Abstract:

    © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The flow-induced noise generated by a rigid cylinder immersed in low Mach number flow is predicted using a hybrid computational fluid dynamics (CFD)-boundary element method (BEM) technique. The fluctuating flow field is obtained using an incompressible CFD solver. A high-order reconstruction scheme is used to extract acoustic sources based on Lighthill's acoustic analogy from the flow field data. The Convected Wave Equation is transformed to Helmholtz and Laplace Equations, with the effect of the mean flow on the scattered acoustic field taken into account using non-uniform potential flow. A periodic BEM technique is used to formulate the acoustic problem as two separate block Toeplitz systems. Solving the aeroacoustic problem using block Toeplitz systems significantly reduces computational time and storage requirements. The generalized minimal residual method is then employed along with the discrete Fourier transform to solve the block Toeplitz systems. The results from the hybrid CFD-BEM technique are presented for turbulent flow past a circular cylinder, with Reynolds number based on the cylinder diameter of ReD= 46000 and Mach number M=0.21. The aeroacoustic results are compared with experimental data from literature

  • Aeroacoustic analysis of a cylinder in low mach number flow using a periodic CFD-BEM technique
    2016
    Co-Authors: Karimi M, Croaker P, Kessissoglou N, Peake N
    Abstract:

    The flow-induced noise generated by a rigid cylinder immersed in low Mach number flow is predicted using a hybrid computational fluid dynamics (CFD)-boundary element method (BEM) technique. The fluctuating flow field is obtained using an incompressible CFD solver. A high-order reconstruction scheme is used to extract acoustic sources based on Lighthill's acoustic analogy from the flow field data. The Convected Wave Equation is transformed to Helmholtz and Laplace Equations, with the effect of the mean flow on the scattered acoustic field taken into account using non-uniform potential flow. A periodic BEM technique is used to formulate the acoustic problem as two separate block Toeplitz systems. Solving the aeroacoustic problem using block Toeplitz systems significantly reduces computational time and storage requirements. The generalized minimal residual method is then employed along with the discrete Fourier transform to solve the block Toeplitz systems. The results from the hybrid CFD-BEM technique are presented for turbulent flow past a circular cylinder, with Reynolds number based on the cylinder diameter of ReD= 46000 and Mach number M=0.21. The aeroacoustic results are compared with experimental data from literature

Peake N - One of the best experts on this subject based on the ideXlab platform.

  • Acoustic scattering for rotational and translational symmetric structures in nonuniform potential flow
    2017
    Co-Authors: Karimi M, Croaker P, Peake N, Kessissoglou N
    Abstract:

    © Copyright 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. An efficient approach is proposed to predict acoustic scattering with nonuniform potential flow effects for structures with rotational and translational symmetries. The Convected Wave Equation is transformed to Helmholtz and Laplace Equations using a time transformation. The boundary-element method is used to formulate scattering by rotationally symmetric structures as two separate block circulant matrix Equations and, similarly, as two separate block Toeplitz matrix Equations for structures with translational symmetry. Discrete Fourier transform is employed to solve the block circulant systems. The block Toeplitz systems are solved using the generalized minimal residual method along with the discrete Fourier transform. Solving the Convected Wave Equation using structured matrices significantly reduces computational time and storage requirements. To demonstrate the application of the formulation, two exterior acoustic case studies are considered. The first case study examines acoustic scattering from a sphere submerged in potential flow under monopole source excitation. Directivity plots obtained using the proposed technique are compared with analytical results. The second case study examines flow-induced noise generated by a rigid cylinder immersed in low-Mach-number flow, with the effect of mean flow on the scattered acoustic field taken into account using nonuniform potential flow. The fluctuating flowfield is obtained using an incompressible computational fluid dynamics solver. Acoustic sources based on Lighthill's analogy are extracted from the flowfield data using a high-order reconstruction scheme. Results from the hybrid computational fluid dynamics-boundaryelement method technique are presented for turbulent flow past the cylinder, with Reynolds number based on cylinder diameter of ReD = 46;000 and Mach numberM = 0.21. The aeroacoustic results are compared with data from literature

  • Aeroacoustic analysis of a cylinder in low mach number flow using a periodic CFD-BEM technique
    2016
    Co-Authors: Karimi M, Croaker P, Kessissoglou N, Peake N
    Abstract:

    © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The flow-induced noise generated by a rigid cylinder immersed in low Mach number flow is predicted using a hybrid computational fluid dynamics (CFD)-boundary element method (BEM) technique. The fluctuating flow field is obtained using an incompressible CFD solver. A high-order reconstruction scheme is used to extract acoustic sources based on Lighthill's acoustic analogy from the flow field data. The Convected Wave Equation is transformed to Helmholtz and Laplace Equations, with the effect of the mean flow on the scattered acoustic field taken into account using non-uniform potential flow. A periodic BEM technique is used to formulate the acoustic problem as two separate block Toeplitz systems. Solving the aeroacoustic problem using block Toeplitz systems significantly reduces computational time and storage requirements. The generalized minimal residual method is then employed along with the discrete Fourier transform to solve the block Toeplitz systems. The results from the hybrid CFD-BEM technique are presented for turbulent flow past a circular cylinder, with Reynolds number based on the cylinder diameter of ReD= 46000 and Mach number M=0.21. The aeroacoustic results are compared with experimental data from literature

  • Aeroacoustic analysis of a cylinder in low mach number flow using a periodic CFD-BEM technique
    2016
    Co-Authors: Karimi M, Croaker P, Kessissoglou N, Peake N
    Abstract:

    The flow-induced noise generated by a rigid cylinder immersed in low Mach number flow is predicted using a hybrid computational fluid dynamics (CFD)-boundary element method (BEM) technique. The fluctuating flow field is obtained using an incompressible CFD solver. A high-order reconstruction scheme is used to extract acoustic sources based on Lighthill's acoustic analogy from the flow field data. The Convected Wave Equation is transformed to Helmholtz and Laplace Equations, with the effect of the mean flow on the scattered acoustic field taken into account using non-uniform potential flow. A periodic BEM technique is used to formulate the acoustic problem as two separate block Toeplitz systems. Solving the aeroacoustic problem using block Toeplitz systems significantly reduces computational time and storage requirements. The generalized minimal residual method is then employed along with the discrete Fourier transform to solve the block Toeplitz systems. The results from the hybrid CFD-BEM technique are presented for turbulent flow past a circular cylinder, with Reynolds number based on the cylinder diameter of ReD= 46000 and Mach number M=0.21. The aeroacoustic results are compared with experimental data from literature

H S Ribner - One of the best experts on this subject based on the ideXlab platform.

  • effects of jet flow on jet noise via an extension to the lighthill model
    Journal of Fluid Mechanics, 1996
    Co-Authors: H S Ribner
    Abstract:

    The Lighthill formalism for jet noise prediction is extended to accommodate Wave transport by the mean jet flow. The extended theory combines the simplicity of the Lighthill approach with the generality of the more complex Lilley approach. There is full allowance for 'flow-acoustic' effects : shielding, as well as the refractive 'cone of (relative) silence'. A source term expansion yields a Convected Wave Equation that retains the basic Lighthill source term. This leads to a general formula for power spectral density emitted from unit volume as the Lighthill-based value multiplied by a squared 'normalized' Green's function. The Green's function, referred to a stationary point source, delineates the refraction dominated 'cone of silence'. The convective motion of the sources, with its powerful amplifying effect, also directional, is accounted for in the Lighthill factor. Source convection and Wave convection are thereby decoupled, in contrast with the Lilley approach : this makes the physics more transparent. Moreover, the normalized Green's function appears to be near unity outside the 'cone of silence'. This greatly reduces the labour of calculation : the relatively simple Lighthill-based prediction may be used beyond the cone, with extension inside via the Green's function. The function is obtained either experimentally (injected 'point' source) or numerically (computational aeroacoustics). Approximation by unity seems adequate except near the cone and except when there are coaxial or shrouding jets : in that case the difference from unity will quantify the shielding effect. Further extension yields dipole and monopole source terms (cf. Morfey, Mani, and others) when the mean flow possesses density gradients (e.g. hot jets).

Lorna J Ayton - One of the best experts on this subject based on the ideXlab platform.

  • acoustic scattering by cascades with complex boundary conditions compliance porosity and impedance
    Journal of Fluid Mechanics, 2020
    Co-Authors: Peter J Baddoo, Lorna J Ayton
    Abstract:

    We present a solution for the scattered field caused by an incident Wave interacting with an infinite cascade of blades with complex boundary conditions. This extends previous studies by allowing the blades to be compliant, porous or satisfy a generalised impedance condition. Beginning with the Convected Wave Equation, we employ Fourier transforms to obtain an integral Equation amenable to the Wiener–Hopf method. This Wiener–Hopf system is solved using a method that avoids the factorisation of matrix functions. The Fourier transform is inverted to obtain an expression for the acoustic potential function that is valid throughout the entire domain. We observe that the principal effect of complex boundary conditions is to perturb the zeros of the Wiener–Hopf kernel, which correspond to the duct modes in the inter-blade region. We focus efforts on understanding the role of porosity, and present a range of results on sound transmission and generation. The behaviour of the duct modes is discussed in detail in order to explain the physical mechanisms behind the associated noise reductions. In particular, we show that cut-on duct modes do not exist for arbitrary porosity coefficients. Conversely, the acoustic far-field modes are unchanged by modifications to the boundary conditions. We apply our solution to a cascade of perforated plates and see that a fractional open area of 1 % is sufficient to significantly attenuate backscattering. The solution is essentially analytic (the only numerical requirements are matrix inversion and root finding) and is therefore extremely rapid to compute.

  • acoustic scattering by cascades with complex boundary conditions compliance porosity and impedance
    arXiv: Fluid Dynamics, 2019
    Co-Authors: Peter J Baddoo, Lorna J Ayton
    Abstract:

    We present a solution for the scattered field caused by an incident Wave interacting with an infinite cascade of blades with complex boundary conditions. This extends previous studies by allowing the blades to be compliant, porous or satisfying a generalised impedance condition. Beginning with the Convected Wave Equation, we employ Fourier transforms to obtain an integral Equation amenable to the Wiener--Hopf method. This Wiener--Hopf system is solved using a method that avoids the factorisation of matrix functions. The Fourier transform is inverted to obtain an expression for the acoustic potential function that is valid throughout the entire domain. We observe that the principal effect of complex boundary conditions is to perturb the zeros of the Wiener--Hopf kernel, which correspond to the duct modes in the inter-blade region. We focus efforts on understanding the role of porosity, and present a range of results on sound transmission and generation. The behaviour of the duct modes is discussed in detail in order to explain the physical mechanisms behind the associated noise reductions. In particular, we show that cut-on duct modes do not exist for arbitrary porosity coefficients. Conversely, the acoustic modes are unchanged by modifications to the boundary conditions. Consequently, we observe that even modest values of porosity can result in reductions in the sound power level of $5$ dB for the first mode and $20$ dB for the second mode. The solution is essentially analytic (the only numerical requirements are matrix inversion and root finding) and is therefore extremely rapid to compute.